Circadian rhythms in diet and habitat use in red ruffed lemurs (Varecia rubra) and white-fronted brown lemurs (Eulemur fulvus albifrons).

Daily variation in niche use among vertebrates is attributed to a variety of factors, including thermoregulatory, reproductive, and nutritional requirements. Lemuriform primates exhibit many behavioral and physiological adaptations related to thermoregulation and sharp, seasonal reproduction, yet they have rarely been subjects of a quantitative analysis of circadian (or daily) rhythms in niche use. In this study, I document daily rhythms in diet and microhabitat use over an annual cycle in two sympatric, frugivorous lemurs, Varecia rubra and Eulemur fulvus albifrons. Data on diet, forest site, and forest height were recorded at 5-min time points on focal animals and divided into three time blocks for analysis (06:00-10:00 hr, 10:00-14:00 hr, and 14:00-18:00 hr). I employed multivariate tests of independence to examine daily rhythms in diet and microhabitat use according to sex, season, and reproductive stage. Throughout the day, V. rubra is frugivorous and dwells in the upper canopy, with notable departures (especially for females) during the hot seasons, gestation, and lactation. E. f. albifrons has heterogeneous daily rhythms of food choice and microhabitat use, particularly across seasons, and both sexes are equally variable. These daily rhythms in diet and microhabitat use appear related to thermoregulatory and nutritional requirements, seasonal food availability and circadian rhythms of plant (and possibly insect) palatability, predator avoidance tactics, and in the case of Varecia, to reproduction. Daily rhythms of food choice in V. rubra support two previously suggested hypotheses explaining why primates consume more nonfruit items late in the day, whereas those of E. f. albifrons are too variable to lend support to these hypotheses. Copyright 2003 Wiley-Liss, Inc.